Surgical instruments with rotating cutting burrs to dissect and cut bone long have been employed in the medical arts. For instance, craniotomes are surgical instruments employed in the surgical procedure known as craniectomy. Craniectomy involves opening the skull so that access may be had to the brain to perform neurosurgery or the like.
Craniotomes often are used in the correction of scaphocephaly. Scaphocephaly, or boat-shaped head, is a cranial dysmorphia that may be immediately apparent at birth, and becomes more difficult to correct with advancing age. This condition is caused by premature craniosynostosis, or fusion of the cranial sutures, specifically, the saggital suture. Although neurological signs and symptoms have been reported in untreated cases, the only clear indication for surgical correction of scaphocephaly is cosmesis. If not treated, children with scaphocephaly can be the subject of unpleasant discrimination by peers and may have significant psychosocial problems. Surgical correction should be recommended for most, if not all, children who have this cranial dysmorphia.
Many treatments for scaphocephaly have been proposed. See, e.g. Greene, Jr., et al., "Treatment of Scaphocephaly with Sagittal Craniectomy and Biparietal Morcellation," Neurosurgery 23:2, 196-202 (1988); Olds, "Surgical Treatment of Sagittal Synostosis," Neurosurgery 18:3, 345-347 (1986); Sutton et al., "Total Cranial Vault Reconstruction for the Older Child with Scaphocephaly," Pediatr. Neurosurg. 1993:19, 63-72 (1993); McComb, "Occipital Reduction-Biparietal Widening Technique for Correction of Sagittal Synostosis," Pediatr. Neurosurg. 1994:20 99-106 (1994); Marsh et al., "Surgical Management of Sagittal Synostosis," Neurosurgery Clinics of North America 2:3, 629-640 (1991). In the simplest of these treatments, a strip at the center of the skull is surgically removed, thereby allowing the skull to expand under pressure of the expanding brain. For example, wide sagittal craniectomy with or without biparietal outfracture is a preferred procedure when the patient is very young (under age six months). In such infants, the pressure of the expanding brain causes the skull to reshape itself. The cranial bone ultimately grows back and fuses to thereby reform the complete skull.
When the patient reaches an older age, such as about nine to twelve months, craniectomies become much more difficult to perform. The brain no longer expands at a rate sufficient to reshape the skull, and the skull itself has thickened to such an extent that it may not remodel significantly. Moreover, the skull may not reossify after surgery, thus requiring reconstruction of the skull. F o r such patients, more radical procedures must be used to force the skull to reshape itself. For example, in the subtotal craniectomy procedure, a portion of the skull is removed and physically reshaped by the surgeon, then replaced.
All of the foregoing procedures generally are accomplished by means of a conventional surgical drill, which typically includes a handle and a cutting means for cutting the skull of a patient. The dura mater, or dura, is a tough membrane that surrounds the brain in mammals. Generally, a surgeon should not pierce this dura in operations to correct scaphocephaly. Accordingly, conventional surgical instruments include a guard for preventing the cutting means from piercing the dura of the patient.
In performing an operation using such previously available drills, the scalp of the patient is completely reflected from the skull. This process entails incising the scalp near the center and pulling the scalp flaps to either side or front and back, thus completely exposing the skull. An incision is made in the skull, and the surgical drill is then used to remove portions of the skull.
Use of such a conventional surgical drill suffers from a number of drawbacks, however, which the present invention seeks to overcome. These disadvantages stem from the aforementioned need to completely reflect the scalp from the skull of the patient. For instance, upon conclusion of the craniectomy when the scalp flaps have been reflected, the scalp must be sewn shut. This may cause scarring and creates additional risk of infection. In addition, increased surgical time is required to open and close longer incisions. Increased blood loss and post operative swelling, resulting in longer hospital stays, are further disadvantages.
In addition, many surgeons are reluctant to reflect the scalp from very young infants, such as age four months. Surgical correction of scaphocephaly is preferred at as early an age as is surgically permissible, inasmuch as the brain most rapidly expands during the earliest months. If a surgeon is reluctant to perform a craniectomy on a patient because of the need to reflect the scalp, this reluctance may prevent the surgeon from performing a craniectomy until the patient has reached an age of several months. The patient may then require a more radical surgical procedure than that previously required.
A prior art surgical instrument is shown in FIG. 1. Such instruments are available, for example, from MIDAS REX.RTM. PNEUMATIC TOOLS, INC., Fort Worth, Tex. The instrument 20 comprises a handle 21 including a side-biting burr 22. The tip 23 of the burr 22 is protected by a guard 24 having a laterally extending foot 25, which prevents the tip 23 from piercing the dura of a patient. The burr 22 is powered by a drive shaft extending through an axial bore in the handle 21. The drive shaft is driven by a motor, which is coupled to the operator gripping portion 26 and which typically is driven by a source of compressed air. Such prior art device is exemplified by the device disclosed in U.S. Pat. No. 5,304,191, assigned to MIDAS REX.RTM. PNEUMATIC TOOLS, INC. Because the side-biting burr extends from the handle at a direction generally coaxial with the axis of the handle, the surgeon cannot access the scalp without reflecting scalp flaps from the patient.
To avoid these shortcomings, it is a general object of the present invention to provide a surgical instrument useful in the performance of cranial surgery that avoids the need to reflect the scalp from the skull of the patient. Another object is to provide a guard for a surgical saw which deflects and protects the dura during cranial surgery without the need to reflect the scalp. A further object of the present invention is to provide a method for cranial surgery, which method avoids the need to reflect the scalp.